In recent years cellular and mobile phones have become increasingly popular. A cellular telephone is merely one example of what is referred to in telecommunications as a “mobile station”. In general, a mobile station (MS) has two components: a mobile terminal (MT), which is typically a handset used to access the radio interface as a radio modem, and a terminal equipment (TE) which is typically a laptop or a Personal Digital Assistant (PDA). However, a mobile station may have the combined functionalities of a mobile terminal and terminal equipment. Thus, a mobile station (MS) can take on various forms other than a cellular (mobile) telephone, including a computer (e.g., a laptop computer) with mobile termination capabilities. Telecommunications services, including wireless Internet access, are provided between a mobile (or wireless) communications system (e.g., a cellular telecommunications network) and a mobile station over an air interface, e.g., over radio frequencies.
To satisfy recent subscriber demands for wireless Internet access and to develop third generation (3G) networks (including the development of Universal Mobile Telephone Service (UMTS) networks), many GSM operators are introducing General Packet Radio Service (GPRS). GPRS is considered as a service or feature of GSM. It was designed by ETSI (European Telecommunications Standards Institute) to be implemented over the existing infrastructure of GSM without interfering with the already existing services. This technology increases the data rates of existing GSM networks, allowing transport of packet-based data. GPRS is one major development in the GSM standard that benefits from packet switched techniques to provide mobile subscribers with the much needed high bit rates for bursty data transmission applications such as Web browsing. Thus, GPRS provides mobile subscribers with access to data communication applications such as electronic mail, corporate intranet networks, and the Internet using their mobile stations. Unlike circuit-switched second generation (2G) technology, GPRS is referred to as a so-called “always-on” service, allowing GSM operators to provide high speed Internet access at a reasonable cost by billing mobile station users for the amount of data they transfer rather than for the length of time they are connected to the network.
Here, it should be noted that the present disclosure is mainly concerned with packet data transfers in a mobile communications system. Thus, voice calls and the signal processing associated therewith are not described in great detail. Furthermore, signal processing, protocols, and other procedures for simultaneously handling data packets and voice calls are also not explained in depth so that the features data packet transfers are not obscured.
Existing GSM networks use circuit-switched technology to transfer information (voice or data) between users. However, GPRS (and developing UMTS networks) uses packet switching and a physical channel is dynamically established only when data is being transferred. Once data has been transferred, the channel resource (a timeslot or the air interface) can be re-allocated to other users for more efficient use of the network.
When packet-switched data leaves the GPRS/GSM network, it is transferred to TCP-IP (Transmission Control Protocol—Internet Protocol) networks such as the Internet or X.25. Thus, GPRS includes new transmission and signaling procedures as well as new protocols for interworking with the Internet Protocol (IP) environment and other standard packet networks.
A mobile (or wireless) communications system can comprise various elements including a switching network and mobile station in communication therewith. In particular, GPRS technology uses existing GSM networks (a type of switching network) and adds new packet-switching network elements.
FIG. 1 depicts a logical architecture of a GPRS network. Although one skilled in the art would understand the various network elements (including protocols, interfaces, etc.) comprise the GPRS network, only certain relevant network elements will be described in detail herein.
There are mobile stations (MS) 2, each having a mobile terminal (MT) 4, which is typically a handset used to access the radio interface as a radio modem, and a terminal equipment (TE) 6. Each mobile station 2 is in communication with a Base Station Subsystem (BSS) 10, performing radio-related (e.g., wireless air interface) functions, which comprises a Base Transceiver Station (BTS) 12 and a Base Station Controller (BSC) 14. The BTS 12 handles the radio interface to the MS 2, while the BSC 14 provides control functions and physical links
The BSS 10 is operatively connected with a Network Switching System (NSS) 20, which is responsible for call control, service control and subscriber mobility management functions. The BSS 10 comprises a Home Location Register (HLR) 22, a Mobile Switching Center (MSC) 24 and a Visitor Location Register (VLR) 26. The HLR 22 is a database storing and managing permanent data about the subscribers, including service profiles, location information, and activity status. The MSC 24 is responsible for telephony switching functions of the network, among various other functions. The HLR 22 and MSC 24 are connected via a so-called Map-D interface. The VLR 26 is a database used to store temporary data about the subscribers and is needed by the MSC 24 for servicing visiting subscribers.
A network element introduced by GPRS is the GPRS Support Node (GSN), which is necessary for the GSM network to support packet data service. There are two types of GSNs: an SGSN (serving-GSN) 28 and a GGSN (Gateway-GSN) 29.
The SGSN 28, which like the GSM mobile switching center and visitor location register (MSC 24/VLR 26), controls the connection between the network and the MS 2. The SGSN 28 provides session management and GPRS mobility management functions such as handovers and paging, and also counts the number of packets routed. The SGSN 28 attaches to the home location register HLR 22 via a so-called Gr interface and to the MSC 24/VLR 26 via a so-called Gs interface. Also, the SGSN 28 connects with other SGSNs 28 and GGSNs 29 via a so-called Gn interface. Furthermore, the SGSN 28 connects with the BSC 14 via a so-called Gb interface. The GGSN 29 is connected with a network (such as a Packet Data Network PDN) 30. The PDN 30 can be connected with a terminal 40 via a so-called Gi interface allowing users to access the PDN 30.
To initiate packet data transfers, a mobile station 2 must first attach itself to the GPRS network (a type of switching network) by a so-called “activation” procedure whereby a process known as Packet Data Protocol (PDP) context activation is performed. Here, the PDP context assigns an Internet Protocol (IP) address to the mobile station 2 if it has no static address. Upon activation, the mobile station 2 can access the network, request resources, send data, go into standby mode if no data is being transmitted, and repeat the above process over again.
More particularly, a PDP context activates a packet communication session with the SGSN 28. During the activation procedure, the mobile station 2 either provides a static IP address or requests a temporary IP address from the network. It also specifies the Access Point Name (APN) with which it wants to communicate, for example an Internet address or an Internet service provider. The mobile station 2 requests a desired quality of service (QoS) and a Network Service Access Point Identifier (NSAPI). Because the mobile station 2 can establish multiple PDP context sessions for different applications, the NSAPI is used to identify the data packets for a specific application. Then, the SGSN 28 and other elements in the network proceed to establish a connection with the mobile station 2 so that packet data can be transferred therebetween. For a given active PDP context, packet data transfers can be an uplink data transfer (i.e., initiated by the mobile station or mobile-originated) or a downlink data transfer (i.e., initiated by the network or mobile-terminated).
The mobile station 2 specifies its network service access point and the access point name (APN) of the Packet Data Network (PDN) it wants to connect to. The APN specifies the target PDN network identifier such as “intranet.company-name.com” and the operator domain name such as “operator-name.country.gprs”. The SGSN 28 identifies the corresponding GGSN 29 and makes it aware of the mobile station 2. A two-way point-to-point path or a “tunnel”, is uniquely identified by a tunnel identifier (TID) and is established between the SGSN 28 and the GGSN 29. Tunneling is the means by which all encapsulated packets are transferred from the point of encapsulation to the point of decapsulation. In this case, the SGSN 28 and GGSN 29 are the two end-points of the tunnel. At the mobile station 2 side, a PDP context is identified by a network service access point identifier (NSAPI). The mobile station 2 uses the appropriate NSAPI for subsequent data transfers to identify a PDN 30. On the other hand, the SGSN 28 and GGSN 29 use the TID to identify transfers with respect to a specific mobile station 2. Depending on the GPRS implementation, a mobile station 2 can be assigned static or dynamic addresses. For instance, the operator can assign a permanent (static) PDP address to the mobile station 2 or choose to assign a different address for each PDP context activated dynamically. Also, a visited network may assign dynamically an address to the mobile station 2 for each PDP context activated.
FIG. 2 shows a conventional art activation procedure between a mobile station and a switching network (i.e., relevant portions of the GPRS/GSM network) of a mobile communications system when there is a packet call collision. Here, it should be understood that only data transfers involving the so-called “packet calls” are considered. Voice calls may co-exist with packet calls, and call collisions may occur therebetween. However, the handling of collisions between voice calls and packet calls are not described in depth in this disclosure so that the features of handling packet call collisions are not obscured.
A mobile station 100 and a switching network 200 (e.g., the GSM network, the GPRS network, or portions thereof) communicate with one another in order to exchange data packets therebetween. A so-called “packet call” is initiated by either the mobile station 100 or the switching network 200 when transferring data packets.
Here, packet data communications are typically carried out over various GPRS channels. Typically, if an uplink packet transfer (from the mobile station 100 to the switching network 200) is already in progress over a particular channel, a downlink packet transfer (from the switching network 200 to the mobile station 100) is performed over a different channel to avoid the occurrence of packet call collisions. Alternatively, priorities can be assigned to certain types of packet calls such that only an uplink transfer or a downlink transfer is performed over one particular channel.
More specifically, a so-called “packet call collision” can be generally defined as a situation where the mobile station 100 and the switching network 200 simultaneously requests a packet call from one another. For example, packet call collision is considered to have occurred when a mobile station 100 requests a packet call to the switching network 200 (S101) while the switching network 200 simultaneously requests a packet call to the mobile station 100 before transmitting a reply regarding the success or failure in processing the packet call received from the mobile station 100 (S102).
Thereafter, according to the contents of the message received from the switching system 200, the mobile station 100 can ignore the received message sent from the switching system 200 or can send a reject message to the switching system 200 (S103). The switching system 200, upon responding to the packet call request of the mobile station 100 (S104), proceeds to exchange packet data thereafter (S105).
This conventional art method of processing packet call collisions employs a technique of applying a so-called “order of priority” to all packet calls so that those of higher priority are maintained, while those of lower priority are removed. In the conventional art, packet calls originating from the mobile station 100 (i.e., uplink packet calls) are given a higher priority than those originating from the switching network 200 (i.e., downlink packet calls). Thus, when a packet call collision occurs, the packet data transfer procedure continues to proceed with only the packet call originating from the mobile station 100, while the packet calls originating from the switching network 200 are removed or ignored.